1. Field of the Invention
The present invention relates to a swash plate tilting angle detector. More particularly, the present invention relates to a swash plate tilting angle detector for detecting the tilting and rolling angle of a swash plate in a swash plate plunger type hydraulic unit such as a swash plate plunger pump or swash plate plunger motor.
2. Description of the Background Art
Until recently, various types of hydraulic continuously variable transmissions each comprising a combination of a hydraulic pump and a hydraulic motor have been known and implemented. For example, hydraulic continuously variable transmissions disclosed in JP-A 6-2753 and JP-B 7-88884 are proposed by the applicant of the present application. Each of the hydraulic continuously variable transmissions disclosed by these patent documents comprises a swash plate plunger pump, a swash plate plunger motor and a hydraulic closing circuit for connecting the outlet port and inlet port of the swash plate plunger pump to the inlet port and outlet port of the swash plate plunger motor, respectively, wherein a pump swash plate member is driven by an engine, a pump cylinder and a motor cylinder are connected to each other above the output shaft of the engine, the rotation of a motor swash plate member is restricted, and the angle of a motor swash plate can be changed.
In this hydraulic continuously variable transmission, a pump cylinder and a motor cylinder are connected to each other back to back, and pump and motor distributor valves (distributor valves) are arranged in this connection portion to constitute a closed hydraulic circuit. The pump and motor distributor valves supply oil discharged from pump plungers which are reciprocated in the pump cylinder by the revolution of a pump swash plate to be driven into a motor cylinder chamber to push motor plungers so that they are moved in an axial direction in sliding contact with a motor swash plate to drive the motor cylinder.
By changing the angle of the motor swash plate, the reciprocating strokes of the motor plungers, that is, the motor capacity is changed continuously to vary the revolution speed of the motor cylinder continuously. When this speed change control is carried out, the angle of the motor swash plate is detected, and the control of the operation of a motor servo mechanism for controlling the angle of the motor swash plate is based on detection information on the angle of the motor swash plate. Therefore, the detection of the angle of the motor swash plate is necessary. For example, JP-A 2001-343060 discloses that the rotation angle of a swash plate holder is detected by mounting a ratio detection sensor, which is a potentiometer, to a casing.
The above known ratio detection sensor, that is, a swash plate angle detector is mounted to a transmission housing, and a revolution detection axis extending from this detector is secured to the swash plate holder (swash plate rolling member) to transmit the revolution of the swash plate holder turned by the tilting and rolling of the swash plate to the revolution detection axis as the tilting angle of the swash plate. However, as the swash plate angle detector is mounted to the casing, the center of rolling of the swash plate rolling member supported by the casing and the center of the revolution detection axis of the swash plate angle detector may slightly differ from each other. The revolution detection axis is mounted at an angle, accurate angle detection may not be carried out, and a detection error may occur. Therefore, it is necessary to prevent the above difference.
In other words, the swash plate angle detector must be mounted to the casing such that the revolution detection axis of the swash plate angle detector becomes coaxial to the center of rolling of the swash plate rolling member. As a result, the installation position and the installation angle of the swash plate angle detector are limited, thereby reducing the degree of lay-out freedom. That is, to carry out the optimum lay-out of the device, the installation of the swash plate angle detector must be taken into consideration for the lay-out and the degree of lay-out freedom is low.
Although the known devices have utility for their intended purposes, there is still a need to provide an improved swash plate tilting angle detector with greater lay-out freedom.